Joystick method for maneuvering a marine vessel with two or more sterndrive units:
http://www.freepatentsonline.com/7467595.html
Axius:
http://www.brunswickmarine.fi/?nid=39284&lcid=1035
IPS:
Ultra Dynamics:
http://www.smallships.co.uk/d/index.php?pageId=15&aid=118
Hamilton Jet, Blue Arrow: